Portion of touch screen won't respond

Hi, I have an HTC Aria, and ever since yesterday a part of my touch screen won't respond. I didn't drop it or anything though. The part of the screen is above the 'Home', 'Menu', 'Back', and 'Search' buttons, which all work fine. I'e had issues with the touch screen on this phone before. I would be texting and when I pressed the space button it would touch v. Or when I pressed the backspace button, it would go to p. Can someone please tell me if this could be fixed. And if it can, can they do it at the AT&T store. I've had this phone for quite awhile, and I didn't buy it from them. I bought it from a no contract website. Thanks! All answers are greatly appreciated!